1. Field of the Invention
The present invention relates to a system for rapidly warming up a catalytic converter provided to an automotive internal combustion engine by increasing the throttle opening degree and retarding the ignition timing immediately after starting of the engine.
2. Description of the Prior Art
Currently, many internal combustion engines in automobiles are equipped with a catalytic converter for purifying the engine exhaust gas. Almost every catalyst now used for this purpose displays its ability to the extent of practical satisfaction only when it is maintained at a sufficiently high temperature. While the engine is operating under normal conditions, the temperature of the exhaust gas is high enough to allow the catalyst in the catalytic converter to work satisfactorily efficiently. However, the catalyst cannot work satisfactorily when the exhaust gas temperature is relatively low as is usual for some time immediately after cold-starting of the engine. Accordingly, it becomes necessary to provide the catalytic converter or the engine with a warm-up means for promoting warm-up of the catalyst in the catalytic converter to render the catalyst effective as soon as possible after starting of the engine.
As a practical example of hitherto proposed warm-up means for automotive catalytic converters, there is a system which is so constructed as to promote warm-up of the catalyst during idling of the engine immediately after cold-starting by slightly increasing the opening degree of the throttle valve with the intention of supplying an increased quantity of exhaust gas to the catalytic converter and at the same time slightly retarding the ignition timing in order to raise the temperature of the exhaust gas. Usually, a throttle opening device and an ignition timing retarding device in this system are both of a vacuum-operated type having a flexible diaphragm with a vacuum chamber defined on one side of the diaphragm, and these two devices are individually connected to the intake passage at a section downstream of the throttle valve such that vacuum created in the intake manifold can simultaneously be applied to the two devices. An electromagnetic valve is used to admit air into the vacuum passages for these two devices during normal operation of the engine and block the admission of air while the engine is idling and the temperature of the engine or the engine cooling water is below a predetermined temperature.
In practical operation of this warm-up system, however, the throttle opening device and the ignition timing retarding device often fail to simultaneously come into operation, although the electromagnetic valve causes simultaneous application of vacuum to the two devices, because of inevitable differences in operating characteristics between these two devices attributed to dispersions of quality in mass production and variations of the degree of deterioration by aging. For example, a synthetic rubber used as the material of the diaphragms in the vacuum-operated devices is liable to undergo a change in its hardness with the lapse of time, and the rate of the change is considerably variable depending on various factors such as the processing conditions, environmental temperatures, etc. Therefore, there is a strong possibility that the ignition timing retarding device comes into action earlier than the throttle opening device, causing the engine to stall or become unstable. Also it is probable that the action of the throttle opening device precedes the action of the ignition timing retarding device. This sequence is rather favorable insofar as the time lag is adequately small, but when the time lag is too great there occurs unwanted increase in the engine speed with augmentation of noise. When the engine is warmed up to the predetermined temperature and/or the gears of the transmission are shifted from the neutral position, it is not certain whether the two vacuum-operated devices become simultaneously inoperative or either of them becomes inoperative precedent to the other, despite desirableness of the simultaneous reaction of the two devices or slightly earlier reaction of the throttle opening device.